RATIONALE: Nearly 99% of the total content of extraterrestrial metals is composed of Fe and Ni, but with greatly variable trace element contents. The accuracy obtained in the inductively coupled plasma mass spectrometry (ICP-MS) analysis of solutions of these samples can be significantly influenced by matrix contents, polyatomic ion interference, and the concentrations of external standard solutions. METHODS: An ICP-MS instrument (X Series 2) was used to determine 30 standard solutions with different concentrations of trace elements, and different matrix contents. Based on these measurements, the matrix effects were determined. Three iron meteorites were dissolved separately in aqua regia and HNO 3 . Deviations due to variation of matrix contents in the external standard solutions were evaluated and the analysis results of the two digestion methods for iron meteorites were assessed. RESULTS: Our results show obvious deviations due to unmatched matrix contents in the external standard solutions. Furthermore, discrepancy in the measurement of some elements was found between the sample solutions prepared with aqua regia and HNO 3 , due to loss of chloride during sample preparation and/or incomplete digestion of highly siderophile elements in iron meteorites. CONCLUSIONS: An accurate ICP-MS analysis method for extraterrestrial metal samples has been established using external standard solutions with matched matrix contents and digesting the samples with HNO 3 and aqua regia. Using the data from this work, the Mundrabilla iron meteorite previously classified as IAB-ung is reclassified as IAB-MG.

Several optimization techniques have been suggested to improve the signal and precision of analyses by thermal ionization mass spectrometry. Our work shows that tungsten filament is likely the most efficient for ionizing strontium when selecting from tungsten, rhenium, and tantalum filament. Deviations of isotopic ratios could be due to the degradation of the Faraday cups. This disadvantage could be avoided through eliminating the imperfect cup from the cup configuration. The high background produced from usage of rhenium filament could be decreased by cleaning the ion source and baking the source housing. ARTICLE HISTORY